This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A249494 #14 May 17 2022 01:46:08 %S A249494 1,3,5,7,9,10,2,4,6,8,20,21,11,12,22,23,13,14,24,25,15,16,26,27,17,18, %T A249494 28,29,19,30,40,41,31,32,42,43,33,34,44,45,35,36,46,47,37,38,48,49,39, %U A249494 50,60,61,51,52,62,63,53,54,64,65,55,56,66,67,57,58,68,69,59,70,80,81,71,72,82,83,73,74,84,85,75,76,86,87,77,78,88,89,79,90,200 %N A249494 Lexicographically earliest permutation of the positive integers such that the parity of the first digit of a(n+1) equals that of a(n)'s last digit. %C A249494 See A249506 for the inverse permutation. %C A249494 See A249278 (and inverse A249279) for the variant based on nonnegative integers. A162501 is a variant based not on parity but on equality. %H A249494 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A249494 (PARI) a(n,a=1,u=0)=for(n=1,n,for(k=1,9e9, !bittest(u,k)&& k\10^(#Str(k)-1)==Mod(a,2)&& !print1(a=k",")&& break);u+=1<<a);a \\ highly unoptimized %Y A249494 Cf. A249506 (inverse permutation), A249278 (variant starting with 0), A249279 (inverse thereof), A162501 (variant based on equality of digits). %Y A249494 Cf. A000030 (initial digit), A010879 (final digit of n). %K A249494 nonn,base %O A249494 1,2 %A A249494 _M. F. Hasler_, Oct 30 2014